Tip heater for a runnerless injection molding probe

ABSTRACT

This invention relates to a tip heater for a runner-less injection molding heating probe and to methods for constructing and repairing the same. The tip heater comprises a generally conical shaped tip, a heating wire, insulating material, and a cap. The tip heater is attached to a heating probe positioned within resin channels communicated to mold cavities. The tip heater is characterized by removable and replaceable tips and/or caps which allow the tip heater to be repaired.

BACKGROUND OF THE INVENTION

This invention relates to a heat-generating device for molds ofinjection molding machines and, more specifically, to a tip heater foruse on a runnerless injection molding heating probe.

Conventional heat-generating devices commonly called torpedoes or probesfor runnerless injection molding are disclosed in U.S. Pat. Nos.4,516,927 and 4,643,664 to Yoshida. These patents disclose pointedheat-generating devices in which a heat-generating wire disposed withina bore in a non-processed cylindrical material is joined to thenon-processed cylindrical material by fusion to form an alloy. The alloyportion is then machined to form a point. The alloy point is commonlycalled a "tip heater". Tip heaters of the type disclosed by Yoshida arerelatively easy to construct; however, tip heaters constructed by fusingthe heating wire to a non-processed cylindrical material and thenmachining the alloy to a point have several disadvantages. Alloymaterials which form the tip of conventional tip heaters haveunpredictable hardness due to the fusion process by which the alloy isformed. When molding abrasive resins, it is common for alloy point tipheaters to fail due to wear at the alloy point. A need therefore existsfor a heat generating device which has a tip heater having a knownhardness to match the abrasive environment in which the device is to beused.

Another disadvantage of alloy pointed tip heaters is the tendency forthe alloy material to exhibit microscopic porosity to molten polymerresins. Alloy points often have microscopic pores through which moltenresin can enter into the body of the heating probe resulting in foulingof the probe and associated equipment over time. A need therefore existsfor a probe having a tip heater which is not susceptible to resinporosity.

Another disadvantage of alloy pointed tip heaters is that alloy pointedtip heaters are difficult to repair once the alloy portion becomesdamaged due to wear from molding abrasive resins, accidents, or abuse ofthe molding equipment. The repair difficulty is due to the uncertaintyof determining exactly where the wire is fused to the unprocessedmaterial. Since the exact location of the alloy-to-wire junction isunknown, it is difficult to know how much of the tip must be removed inorder to effect repairs. A need, therefore, exists for a tip heater foruse during runnerless injection molding which provides a pointed portionin which the wire to point junction is known thereby allowing for easytip heater repair.

Accurate placement of wire to point junction also greatly improvesconsistency of thermal performance guaranteeing identical behaviorbetween multiple probes in a mold.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a tip heater for attachmentto a heating probe used for runnerless injection molding in which thetip heater point has a known hardness. It is also an object of thisinvention to provide a tip heater which is not subject to resinporosity.

It is also an object of this invention to provide a tip heater having aknown heating wire and point juncture which facilitates tip heaterrepair.

To achieve the foregoing and in accordance with the purposes of thepresent invention as embodied and broadly described herein, the presentinvention provides a tip heater attached to a heating probe having ametal body having a front end, a back end, and a longitudinal bore, theprobe utilized in runnerless injection molding machines for opening andclosing mold gates by ON-OFF switching of the tip heater.

The tip heater comprises a generally conically shaped tip, a cap, aheating wire, and an insulating material. The generally conically shapedtip is attached to the front end of the metal body. The tip has a frontand a back end, and a first and a second longitudinal bore. The firstlongitudinal bore of the tip is aligned with the longitudinal bore ofthe metal body. The cap has a socket and is attached to the front end ofthe tip. The socket is aligned with the second longitudinal bore of thetip. The heating wire has a first end and a second end and is disposedin the bore of the metal body and in the first and second longitudinalbores of the tip. The first end of the heating wire is attached to thecap at the socket and the second end of the heating wire is electricallyconnectable to an ON-OFF switch such that the heating wire heats the capwhen the switch is ON and the heating wire does not heat the cap whenthe switch is OFF. The insulating material is disposed between the boreof the metal body and the heating wire and between the bores of the tipand the heating wire.

In yet another embodiment of this invention, the tip heater is attachedto a heating probe having a metal body having a front end, a back endand a longitudinal bore, the probe utilized in runnerless injectionmolding machines for opening and closing mold gates by ON-OFF switchingof the tip heater. The tip heater comprises a generally conically shapedtip, a heating wire, and an insulating material. The generally conicallyshaped tip is attached to the front end of the metal body. The tip has apointed front end, a back end, a recess and a socket. The socket isaligned with the recess, and the recess is aligned with the longitudinalbore of the metal body. The heating wire is disposed in the bore of themetal body and disposed in the recess of the tip. The heating wire has afirst end and a second end. The first end of the heating wire isattached to the tip at the socket. The second end of the heating wire iselectrically connectable to an ON-OFF switch such that the heating wireheats the tip when the switch is ON and the heating wire does not heatthe tip when the switch is OFF. The insulating material is disposedbetween the bore of the metal body and the heating wire, and between therecess of the tip and the heating wire.

Another aspect of this invention provides a method for constructing atip heater attached to a heating probe.

Yet other aspects of this invention provide methods for repairing tipheaters attached to heating probes.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and form a part ofthe specification, illustrate the embodiments of the present inventionand, together with the description serve to explain the principles ofthe invention.

In the drawings:

FIG. 1 is a partially cut-away sectional view of a heating probe with anattached tip heater.

FIG. 1A is an enlarged, partially, cut-away sectional view of the tipand cap of the tip heater illustrated in FIG. 1.

FIG. 2 is a sectional view of the probe illustrated in FIG. 1 takenalong line 2--2.

FIG. 3 is a partially cut-away enlarged sectional view of the tip heatershowing a device under construction.

FIG. 4 is a partially cut-away enlarged sectional view of the completedtip heater.

FIG. 5 is a cut-away enlarged sectional view of one embodiment of thetip heater cap and tip.

FIG. 6 is a cut-away enlarged sectional view of another embodiment ofthe tip heater tip.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A tip heater 50 of the present invention is shown generally in thecircled area in FIG. 1 attached to a probe 10 also shown generally inFIG. 1. Tip heater 50 is comprised of a generally conically shaped tip16, a heating wire 21, insulating material 23, and a cap 30. Probe 10has generally a cylindrical metal body 11 and a head 15.

Metal body 11 has a front end 12, a back end 13, and a longitudinal bore14. The back end 13 of body 11 is attached to head 15. Head 15 ispositioned such that metal body 11 is disposed within mold resin channel101 as shown in FIGS. 1. Head 15 is shown in FIG. 1 having resinchannels 25 shown in FIG. 2 which are positioned in fluid communicationwith resin channels 102 of a manifold 100. The front end 12 of body 11is attached to tip heater 50. Tip heater 50 includes a generally conicaltip 16 having a first longitudinal bore 17, a second longitudinal bore18, a front end 19, and a back end 20 as shown in detail in FIG. 1A.Back end 20 is attached to front end 12 of body 11. Front end 19 isattached to cap 30. Cap 30 has a generally conical shape and a socket32. Heating wire 21 is disposed within bores 14, 17, and 18 and has afront end 24. Front end 24 of wire 21 is attached to cap 30 at socket32. The back end of wire 24 is electronically connectable to an ON-OFFswitch (not shown). Insulating material 23 such as but not limited tomagnesium oxide or a ceramic sleeve is disposed within bores 14, 17, and18 to separate and thermally insulate heating wire 21 from metal body 11and from tip 16. Electrical current flowing through heating wire 21heats cap 30. An electrical return can be attached to the mold or to theprobe to provide electrical continuity. The flow of electricity throughheating wire 21 is controlled by an ON-OFF switch such that when theON-OFF switch is ON, the electricity flow through wire 21 heats cap 30and when the ON-OFF switch is OFF, electricity does not flow throughwire 21 and cap 30 is not heated. Cylindrical metal body 11 can alsohave one or more body heaters (not shown in the drawings) as are wellknown in the art to maintain the molten state of resin within channel101 and within head channels 25 during each injection molding cycle.

Probe 10 is positioned within resin channel 101 such that molten resinfrom an injection molding machine can flow through manifold channel 102,through head channel 25, into channel 101, through gate 103, and into acavity 104 in the mold.

Tip heater 50 is utilized by an ON-OFF switch electrically connected towire 21 being switched ON resulting in heating wire 21 becoming hot. Asa result, cap 30 becomes hot, melting solidified resin in gate 103.Molten resin under pressure then flows through channels 102, 25, 101,gate 103, and into the mold 104. Anytime after flow through the gates isestablished, the ON-OFF switch attached to wire 21 is switched OFFcausing wire 21 to cease heating. Cooling lines 200 in the mold solidifyresin in the areas adjacent tip 16 and cap 30 thereby closing gate 103yet allowing resin in channels 101, 25, and 102 to remain molten.Closing gate 103 allows the mold to be opened and the molded part to beremoved without molten resin flowing through gate 103, and withoutexcess resin waste attaching to the molded part from gate 103, thus,permitting runnerless molding to occur.

Over time, the flow of molten resin through passages 101 and gate 103can cause tip 16 and cap 30 to abrade and eventually improperly open andclose gate 103. Probe tip heaters can also become damaged throughaccident or abuse often resulting in deformation of the tip heater pointor separation of the heating wire from the heater point resulting inimproper gate closure. Alloy pointed tip heaters are not easily repairedand often necessitate replacement of the entire heating probe when thealloy point is damaged. In addition, if between molding operations,probe users notice that a point on a particular alloy pointed tip heateris not withstanding the wear due to abrasive resin environments, anentire new heating probe must be purchased without any assurance thatthe alloy point on the new probe tip heater will withstand theabrasiveness of the resin environment that the new probe is to be usedin. The instant invention solves this problem by providing a tip heaterwith a pointed cap which is constructed to be repaired and which has apoint with a known hardness to match the resin that the tip heater is tobe used in.

The method for constructing a tip heater of this invention is hereindescribed with reference to FIG. 3. Front end 12 of metal body 11 isjoined to tip 16 by welding or brazing at the adjacent peripheries 40.Wire 21 is then disposed within bores 14, 17, 18. An unprocessed cap 30Uof a material having a known hardness and having a socket 32 is thenplaced adjacent tip 16 such that front end 24 of wire 21 is disposed insocket 32. Unprocessed cap 30U is then joined to tip 16 by welding orbrazing at adjacent peripheries 41 and then insulating material 23 ispacked between bores 14, 17, 18, and wire 21. The unprocessed cap isthen swaged to secure the front end 24 of wire 21 within socket 32 andis then machined to a point to form cap 30 as shown in FIGS. 1, 1A, and4. The invention thus provides a repairable tip heater which overcomesthe problem of unknown point hardness associated with alloy pointed tipheaters by providing a pointed cap having known hardness. Additionally,since the point is not constructed by fusion to form an alloy, the tipheater does not suffer from resin microporosity problems.

The cap, as shown in FIG. 4, can be easily repaired by the method ofcutting through fused circumference 41 or grinding cap 30 off to theknown cap-wire juncture at circumference 41. A repair cap is thenattached to wire 21, joined to tip 16, and ground to a point, thus,eliminating the need to replace the entire device 10 every time cap 30is damaged. Repair is made easy by this invention since the problem ofunknown wire-alloy juncture, which is associated with alloy pointed tipheaters, is eliminated.

If the tip 16 is damaged, the tip 16 can be repaired by cutting througharea 40 and removing tip 16, wire 21, and insulating material 23 frombody 11. A repair wire which is either a new wire 21 or the old wire 21is then inserted into body 11, a new repair tip 16 is joined to body 11at adjacent peripheries 40, a new, unprocessed cap of a material havinga known hardness is attached to the repair wire and is joined to therepair tip. Insulating material is then packed between the repairheating wire and the metal body and between the heating wire and therepair tip. The unprocessed cap is then machined to a point.

Another embodiment of the invention is shown in FIG. 5 where, in lieu ofswaging the heating wire to the caps, the heating wire 21A has athreaded first end 24A attached to a threaded socket 32A in cap 30A. Cap30A shown in FIG. 5 can be repaired by cutting through joinedcircumference 41, unscrewing cap 30A from wire 21A, re-attaching a newrepair threaded cap to wire 21A and joining the repair cap to tip 16.

Another embodiment of the invention is shown in FIG. 6. The tip heatershown in FIG. 6 is comprised of a generally conical shaped tip 16B, aheating wire 21, and insulating material 23. Tip 16B has a point 64, aback end 63, a recess 60, and a socket 61. Back end 13 is joined to themetal body of a probe having a longitudinal bore (not shown). Heatingwire 21 has a first end 24 attached to tip 16B at socket 61 and a secondend electrically connectable to an ON-OFF switch (not shown). Insulatingmaterial 23 is disposed between the bore of the probe metal body andheating wire 21 and between recess 60 of tip 16B and heating wire 21.Point 64 is heated when the ON-OFF switch is ON and is not heated whenthe ON-OFF switch is OFF. To repair this embodiment of the tip heater,the entire tip can be removed by cutting through the area attaching tip16B to a metal body (not shown in FIG. 6) and removing wire 21 andinsulating material 23 from device 10. A repair wire is then insertedinto the probe metal body and into the recess and socket of a repairtip. The repair tip is then joined to the metal body, insulatingmaterial is packed between the repair wire and the metal body andbetween repair wire and the repair tip, and the tip is swaged tocompress the insulating material and to secure the repair wire withinthe socket of the repair tip.

The joining of cylindrical metal bodies to tips and tips to caps can beaccomplished by conventional welding, fusion welding, laser welding, bybrazing, by an electron beam, or by any other means well known in theart so long as the joining of cylindrical bodies to tips and tips tocaps, allows tips and/or caps to be removed and replaced by new repairtips and/or caps as needed. The attachment of heating wires to tips orwires to caps can be accomplished as described herein by swaging or bythreading as well as by cryogenic shrink fitting. Additionally, theheat-generating device described herein has been described as having ahead portion located below the manifold. However, it is within the scopeof this invention that the tip heater can be utilized with other probetypes such as but not limited to probes having heads positioned withinmanifolds or probes having heads positioned on opposite sides ofmanifolds from the tip heaters.

Thus, the invention provides a tip heater for use on a heating probeused for runnerless injection molding which has a point of knownhardness which is not subject to resin porosity and which is easilyrepaired.

While the preferred embodiments have been fully described and depictedfor the purposes of explaining the principles of the present invention,it will be appreciated by those skilled in the art that modification andchanges may be made thereto without departing from the scope of theinvention set forth in the appended claims.

I claim:
 1. A heat-generating device in the form of a tip heaterattached to a heating probe utilized in runnerless injection moldingmachines for opening and closing mold gates by ON-OFF switching of thetip heater, said probe having a metal body having a front end, a backend, and a longitudinal bore, said tip heater comprising:a generallyconical shaped tip attached to said front end of said metal body, saidtip having a front and a back end, and said tip having a first and asecond longitudinal bore, said first longitudinal bore of said tipaligned with said longitudinal bore of said metal body; a cap having asocket, said cap attached to said front end of said tip, said socketaligned with said second longitudinal bore of said tip; a heating wirehaving a first end and a second end, said heating wire disposed in saidbore of said metal body and disposed in said first and secondlongitudinal bores of said tip, said first end of said heating wireattached to said cap at said socket; said second end of said heatingwire electrically connectable to an ON-OFF switch such that said heatingwire heats said cap when said switch is ON and said heating wire doesnot heat said cap when said switch is OFF; and an insulating materialdisposed between said bore of said metal body and said heating wire andbetween said bores of said tip and said heating wire.
 2. Theheat-generating device of claim 1 wherein said tip is removably attachedto said metal body.
 3. The heat-generating device of claim 2 whereinsaid cap is removably attached to said tip.
 4. The heat-generatingdevice of claim 2 wherein said tip is welded to said metal body alongadjacent peripheries of said back end of said tip and said front end ofsaid metal body.
 5. The heat-generating device of claim 2 wherein saidtip is brazed to said metal body along adjacent peripheries of said backend of said tip and said front end of said metal body.
 6. Theheat-generating device of claim 3 wherein said heating wire is attachedwithin said socket of said cap by swaging of said cap to said wire. 7.The heat-generating device of claim 3 wherein said first end of saidheating wire is threaded, wherein said socket of said cap is threadedand wherein said first end of said heating wire is threadably attachedto said socket of said cap.
 8. The heat-generating device of claim 3wherein said heating wire is fixed within said socket of said cap bycryogenic shrink fitting.
 9. The heat-generating device of claim 3wherein said cap is welded to said tip along adjacent peripheries ofsaid cap and said front end of said tip.
 10. The heat-generating deviceof claim 3 wherein said cap is brazed to said front end of said tip. 11.A heat-generating device in the form of a tip heater attached to aheating probe utilized in runnerless injection molding machines foropening and closing mold gates by ON-OFF switching of the tip heater,said probe having a metal body having a front end, a back end, and alongitudinal bore, said tip heater comprising;a generally conical shapedtip attached to said front end of said metal body, said tip having aback end and a pointed front end, said tip having a recess and a socket,said socket aligned with said recess, said recess aligned with saidlongitudinal bore of said body, a heating wire disposed in said bore ofsaid metal body and disposed in said recess of said tip, said heatingwire having a first end and a second end, said first end of said heatingwire attached to said tip at said socket, said second end of saidheating wire electrically connectable to an ON-OFF switch such that saidheating wire heats said tip when said switch is ON and said heating wiredoes not heat said tip when said switch is OFF; and an insulatingmaterial disposed between said bore of said metal body and said heatingwire, and between said recess of said tip and said heating wire.
 12. Theheat-generating device of claim 11 wherein said tip is removablyattached to said metal body.
 13. The heat-generating device of claim 11wherein said wire is fixed within said tip socket by swaging.
 14. Theheat-generating device of claim 11 wherein said wire is fixed withinsaid tip socket by cryogenic shrink fitting.
 15. The heat-generatingdevice of claim 11 wherein said tip is welded to said metal body alongadjacent peripheries of said back end of said tip and said front end ofsaid metal body.
 16. The heat-generating device of claim 11 wherein saidtip is brazed to said body along adjacent peripheries of said back endof said tip and said front end of said body.
 17. A tip heater for use ona heating probe utilized in runnerless injection molding machines foropening and closing mold gates by ON-OFF switching of the tip heater,said probe having a metal body having a front end, a back end, and alongitudinal bore wherein the improvement comprises:a generallyconically shaped tip removably attached to said front end of said metalbody, said tip having a front and a back end, and said tip having afirst and a second longitudinal bore, said first longitudinal bore ofsaid tip aligned with said longitudinal bore of said body; a cap havinga socket, said cap removably attached to said front end of said tip,said socket aligned with said second longitudinal bore of said tip; aheating wire disposed in said bore of said metal body and disposed insaid first and second longitudinal bores of said tip, said first end ofsaid heating wire attached to said cap at said socket; said second endof said heating wire electrically connectable to an ON-OFF switch suchthat said heating wire heats said cap when said switch is ON and saidheating wire does not heat said cap when said switch is OFF; and aninsulating material disposed between said bore of said metal body andsaid heating wire and between said bores of said tip and said heatingwire.
 18. A tip heater for use on a heating probe utilized in runnerlessinjection molding machines for opening and closing mold gates by ON-OFFswitching of the tip heater, said probe having a metal body having afront end, a back end, and a longitudinal bore wherein the improvementcomprises:a generally conically shaped tip removably attached to saidfront end of said cylindrical metal body, said tip having a pointedfront and a back end, said tip having a recess and a socket, said socketaligned with said recess said recess aligned with said longitudinal boreof said cylindrical body; a heating wire disposed in said bore of saidmetal body and disposed in said recess of said tip, said heating wirehaving a first end and a second end, said first end of said heating wireattached to said tip at said socket; said second end of said heatingwire electrically connectable to an ON-OFF switch such that said heatingwire heats said tip when said switch is ON and said heating wire doesnot heat said tip when said switch is OFF; and an insulating materialdisposed between said bore of said metal body and said heating wire andbetween said recess of said tip and said heating wire.
 19. A tip heaterattached to a heating probe utilized in runnerless injection moldingmachines for opening and closing mold gates by ON-OFF switching of thetip heater, said probe having a metal body, said tip heater comprising:atip having a bore, said tip removably attached to said metal body ofsaid probe; a pointed cap having a socket, said cap removably attachedto said tip; a heating wire disposed in said tip bore and attached tosaid cap at said socket; and insulating material disposed between saidtip bore and said heating wire; wherein said cap has a known hardness,said cap and said tip are impermeable to polymer resin, wherein said tipis removably attached to said metal body and wherein said cap isremovably attached to said tip to facilitate tip heater repair.